<p>
  In the last chapter we discussed random variables and random distributions. Now we are going to use the distributions we learned to test our hypothesis and also to model the financial data. When building a trading strategy, it's essential to do some research. However, you won't be able to test your idea using all the data, because it's infinity. You can only use a <strong>sample</strong> to do your experiment. That's why we need to understand the difference between population and sample, and then use confidence interval to test our hypothesis.
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<p>
  As we mentioned before, both mean and standard deviation are <strong>point estimation</strong>, and they can be deceiving because sample means are different from population means. Financial data is generated every day now and in the future, thus even though we can use all the data available, it's still just a sample. This is why we need to use confidence interval to attempt to determine how accurate our sample mean estimation is.
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